Thread: MACRO-need help

i write some code. the code is like this:

Code:

#include <stdio.h>
#include <stdlib.h>
#define CHECK(x) if((x>=48)&&(x<=57))\
                    printf("It's a number.\n");\
                else if((x>=65)&&(x<=90))\
                    printf("It's a Upper case letter.\n");\
                else if((x>=97)&&(x<=122))\
                    printf("It's a lower case letter.\n");\
                else\
                    printf("it's a symbol\n");

#define MINM(x,y) if(x>y)\
                        (x);\
                    else\
                        (y);

int main()
{
    char i;
    int j,k,l;
    scanf("%c", &i);
    CHECK(i);
    scanf("%d %d",&j,&k);
    l=MINM(j,k);
    printf("%d is the biggest",l);
    return 0;
}

but, when i compiled it, the compiler is saying that "error: syntax beffore if" in line 24.
can someone help me to find out what's wrong with my code?

> l=MINM(j,k);
This expands to l = if ( j > k )
Does that make any sense to you.

I hope this macro abuse is just an exercise.

It could have said "RHS of expression does not evaluate to an int".

"syntax error" is a general catch-all meaning "something's wrong, you figure it out".

Right hand side.


Quzah.

If you must do macros in this horrible manner, use the ternary operator ?:.

For a contrived and useless example of its usage:

Code:

int bleh(int x)
{
    return x>=0?1:0;
}

This would return 1 if x>=0 and 0 otherwise.

>> yes, this is just an exercise

Good, because this is a really bad idea. Consider what happens if you invoke it like so:

Code:

CHECK(x++);

Anyway, one hack you can use is to enclose all of the statements in a

Code:

do{/*bunch of statements*/}while(0)

.

Code:

#define CHECK(x) if((x>=48)&&(x<=57))\
                    printf("It's a number.\n");\
                else if((x>=65)&&(x<=90))\
                    printf("It's a Upper case letter.\n");\
                else if((x>=97)&&(x<=122))\
                    printf("It's a lower case letter.\n");\
                else\
                    printf("it's a symbol\n");

This is definitely and absolute MACRO ABUSE - you deserve what's coming to you if you write code like this. This should be a function.

Macros that as more than one line should be avoided unless there REALLY is no other way (and even then, there's USUALLY a way to use a SIMPLE macro and a function).

I use macros for three purposes:
1. to use the preprocessor to optionally (not) produce source code (e.g. ifdef/ifndef for debug code or in header guards)
2. Debug code that needs line-number and filename info.
3. Initializations/identifications where a macro can produce extra information from for exampe the name of a variable.



--
Mats

4. For great fun and amusement.


Quzah.

Originally Posted by quzah

4. For great fun and amusement.


Quzah.

Oh, yes for obfuscation in homework and such!

--
Mats